1. Field of the Invention
The present invention relates to a heat insulating glass plate for use in buildings or vehicles, and more particularly to a glass plate with a heat insulating multilayer coating, which has a gray color and is fairly low in transmittance for solar radiation and fairly high in transmittance for radio waves.
2. Description of the Prior Art
Hitherto, various heat insulating multilayer coatings have been proposed to be formed on a transparent glass plate. For example, JP-A-60-36355 discloses a heat reflecting three-layer coating consisting of a first layer of an oxide of a metal selected from Sn, Ti and Al, a second layer of chromium nitride, and a third layer of a dielectric material. The first layer has an optical thickness ranging from 20 to 280 nm. The second layer has a geometrical thickness ranging from 10 to 40 nm. The coated glass plate has a transmittance ranging from 5 to 40% for the visible light. Color of light reflected from the uncoated side of the glass plate is adjusted by the optical thickness of the first layer.
JP-A-3-208837 discloses a heat insulating four-layer coating consisting of a first layer of SiOx or Al.SiOx, a second layer of TiNx, a third layer of TiOx, and a fourth layer of SiOx or Al.SiOx. The four-layer coating is formed on a transparent glass plate by the sputtering method. The first to fourth layers have thicknesses of 10-30 nm, 10-40 nm, 0-20 nm and 30-50 nm, respectively. Light reflected from the uncoated side of the glass plate has a bluish color.
JP-A-3-252332 discloses a heat reflecting three-layer coating with low reflectance for radio waves, which is formed on a transparent glass plate. The three-layer coating consists of first and third layers of colored dielectric films having a surface resistivity not lower than 10.sup.4 M.OMEGA./.quadrature. and a second layer interposed between the first and third layers. The second layer is a metal film or a metal nitride film, and has a surface resistivity not lower than 200 .OMEGA./.quadrature.. Light reflected from the uncoated side of the glass plate has a blue color or a golden color. However, in view of recent strict demand for low reflectance for radio waves, reflectance of the three-layer coating for radio waves is still unsatisfactory.
Recently, a so-called shade band has been proposed to be formed on an upper end portion of a front windshield of an automobile for the purpose of lowering glare of the sunshine. The shade band of the front windshield is usually prepared by incorporating a colorant into an interlayer (polyvinyl butyral film) of a laminated glass plate. For example, it is desired to have a shade band having a gray color which is in harmony with the color of automobile interior and the color of automobile windshields. However, the above-mentioned three publications disclose multilayer coatings which provide the glass plates with colors other than gray color.